Investigation of the compression behaviour of foamed polypropylene sheet samples used for thermoformed cups

Foamed materials are used in many everyday objects, including hot and cold beverage cups. In this research study, the compression behaviour of foamed polypropylene sheet samples used for thermoformed cups is investigated using finite element simulations. Computed tomography (CT) is utilised to examine the microstructure of two extrusion foam sheet samples prior to thermoforming. The samples consist of highly non-uniform cells. Therefore, finite element meshes are created directly from the CT measurements to reproduce the microstructure in detail. The meshes can be used for the mechanical characterisation. In order to validate the simulation models, experimental tensile tests are carried out, as compressive tests are not possible experimentally due to the small thickness of the samples. The validation shows that the tension behaviour in extrusion direction can be well depicted by the microstructural models. One validated model is then used to evaluate the compression behaviour at different stretching degrees to replicate the mechanical behaviour after the thermoforming process. The results show that the stretching of the foam highly affects the compression properties, so the higher the stretching, the lower the compressive strength.